Defferre was never the type of candidate that would personally approve of an alliance with the PCF (he'd rather eat his left arm than endorse a Communist, imo) nor would the PCF also approve of it.

Defferre, however, was a better candidate for an alliance with the centre, though maybe more in 1965.

IIRC, an alliance a la 1965/1974 between the FGDS-left and the PCF was never realistically on the table.

Right.In 1969, Rocard took the place of PMF, sort of. PMF refused everything in the 5th Republic constitution, even to take part in elections (even in order to change all this)...

Kalwejt's scenario is very highly unrealistic. But, in this hypothesis, Defferre would have made it to the 2nd round (as Pinay wouldn't have been efficient in picking centrist votes), but would have been trounced by Pompidou, almost 58-47.

To be a bit more complete, let's say that,in 1969, the young leftists considered the PCF as a traitor party (because of Grenelle agreements between CGT leader Séguy and Pompidou- Balladur-Chirac)and that the mainstream left-centre-left tried to connect with 68 youth but failed in it:PMF refused to go, on the one hand, the old SFIO was completely sidelined, on the other hand.There wasn't any plan for unifying the left. On the contrary, the left was exploded and the official left began to rebuild only in 1971.